When turbines are used on aircraft or for power generation, they are typically run at a temperature as high as possible, for increased operating efficiency. Since high temperatures can damage the alloys used for the components, a variety of approaches have been used to raise the operating temperature of the metal components. One approach calls for the incorporation of internal cooling channels in the component, through which cool air is forced during engine operation. The cooling holes can be formed in the substrate by techniques such as water jet processing and/or electrical discharge machining (EDM). Cooling air (usually provided by the engine's compressor) is fed through the holes from the cooler side to the hot side of the combustor wall. As long as the holes remain clear, the rushing air will assist in lowering the temperature of the hot metal surface and preventing melting or other degradation of the component.
Another technique for protecting the metal parts and effectively raising the practical operating temperature of an aircraft engine involves the use of a thermal barrier coating (TBC). The TBC is usually ceramic-based. TBC systems frequently also include a bond coat which is placed between the ceramic coating and the substrate to improve adhesion. The use of TBC's in conjunction with the battery of cooling holes is sometimes the most effective means for protecting an engine part. However, incorporation of both systems can be very difficult. For example, the cooling holes sometimes cannot be formed in the engine part after a TBC has been applied, since lasers usually cannot effectively penetrate both the ceramic material and the metal to form the pattern of holes. If the cooling holes are formed prior to the application of the TBC system, they may become covered and at least partially obstructed when the bond coat and/or TBC is applied. Additionally, repair of the metal parts often includes replacing the TBC, during which the existing cooling holes may become covered and at least partially obstructed. Complete removal of the ceramic-metal material from the holes can be very time-consuming and ineffective. Any obstruction of the holes during engine operation can interfere with the passage of cooling air, can waste compressor power, and can possibly lead to engine component damage due to overheating.
Therefore methods of coating a component and methods of forming apertures or holes in coated components that do not suffer from the above drawbacks are desirable in the art.